Permeabilizing by acidizing oil shale tuffaceous streaks in and oil recovery therefrom



Dec. 2, 1969 M. PRATs 3,481,398

PERMEABILIZING BY ACIDIZING OIL SHALE TUFFACEOUS STREAKS IN AND OIL RECOVERY THEREFROM Filed Feb. 28, 19e? INVENTORI MICHAEL PR BY: @Sb

HIS AGENT United States Patent O U.S. Cl. 166-251 3 Claims ABSTRACT OF THE DISCLOSURE A method of increasing permeability of oil shale containing tufaceous streaks for recovery of fluidizable materials therefrom comprising acidizing said streaks to form horizontal permeable channels communicating at least one pair of wells.

The present invention relates to a process for creating underground horizontal channels in oil shale for improved recovery of uidizable materials such as hydrocarbons therefrom. More particularly, the present invention relates to establishing by acidization at substantial depth in underground oil shale formations permeable and/or porous horizontal channels between at least one pair of Wells penetrating oil shale formations, through which channels uid flow can be established for the recovery of fluidizable materials, e.g., hydrocarbons, therefrom through a production well(s) It is well known in the art that recovery of shale oil from oil shale by mining and processing it above ground is costly an-d presents many undesirable disposal problems for the by-products. Recovery of oil directly from the underground formation is therefore preferable for many obvious reasons, but because of the impermeability of such formations in situ oil recovery is diicult or impractical. Although such means of recovery of shale oil are known to the art as evident by reference to U.S. Patents 2,969,226; 3,139,928 or 3,233,668, they are generally impractical Ibecause they are costly, ineffective and present other undesirable problems. Also increasing productivity of shale oil by rendering the formation more permeable by establishing fractures or Caverns by mechanical or explosive means or the like have been found to be undesirable since generally such means establish vertical fractures and communication between a pair of wells is difficult to establish.

It is an object of the present invention to recover fluidizable materials, e.g., oil, from oil shale formations penetrated by at least one pair of wells. It is another object of the present invention to render impermeable oil shale formations penetrated by at least one pair of wells sufliciently permeable so that oil recovery therefrom can be established. Still another object of the present invention is to establish permeable channels in oil shale penetrated by wells which are in communication with the permeable channels. Still further, it is an object of the present invention to establish wells into an oil shale having tuffaceous streaks and acidizing said streaks so as to render them permeable and thereby establish receptivity of the formation to fluid recovery.

It has now been discovered that impermeable oil shale formations can be rendered sufficiently permeable by establishing horizontal channels extending through the oil shale formation between at least one pair of wells ice that encounter the shale in a locality in which the tectonics favor vertical fracturing by acidization of particular portions of said formations. The permeable horizontal channels .connecting a pair of wells through which uid commumcation can be effectively established is accomplished by acidizing particularly tuffaceous streaks in the oil shale formation.

The desired permeability in formations penetrated by a pair of wells under disussion can be formed by carrying out the following steps:

(l) Measuring, in each of the wells, the variations with depth of a physical property of earth formation that is responsive to the permeability of the earth formations;

(2) Establishing, in the wells, fluid communication with at least one layer within an interval of oil shale that exhibits a permeability greater than the average permeability of the shale and is encountered in both wells; and,

(3) Pumping a selectively effective acid or acid producing material through said layer between the wells until the permeability within the layer becomes such that, when the layer is filled with liquid and the pressure in one well is increased by an amount insufficient to fracture the formation, the pressure increase is reflected in the other well. Where the treated streaks are several inches thick, the treatment creates permeable channels that are suitable for use in steam drives or soaks, underground combustion drives or solvent displacement oil production processes. Where fracturing is desirable, the fractures can be formed by filling such a permeable channel with liquid and increasing the pressure on the liquid to a pressure sufficient to both support the weight of the overburden and part the rock matrix along said layer. Alternatively, a layer within the oil shale can be fragmented to form a horizontally-extensive layer of interconnecting fractures, by filling such a permeable channel with a liquid explosive and detonating the explosive.

The process of the present invention provides a method for establishing fluid communication between wells and is particularly suitable for establishing such communication where the regional tectonics tend to prevent the formation of horizontal fractures. Such regional tectonics exist, for example, in the oil shales encountered in the Piceance Basin, Colo., the Uinta Basin, Utah and the Green River Basin, Wyo. In such oil shales the bulk of the matrix is very impermeable and horizontal fractures that extend over large distances are impossible or difiicult to establish by simply pressurizing a liquid that is confined within the borehole of a well.

Fluid communication between wells in formations under discussion can be established by the process of the present invention by finding tufiaceous streaks in the formation and injecting therein a delayed or selectively retarded acid that aci-dizes these streaks selectively and converts them to permeable channels. Normally the tuffaceous streaks in these formations are quite thin. This is advantageous in that the acid volumes used to form a permeable channel extending between neighborhood wells does not present a cost recovery factor.

The tuffaceous streaks or zones in oil shales are cornposed predominantly of silicates, e.g., feldspar, quartz and some calcareous materials which have been found to be effectively rendered permeable by suitable acidization. The acidizing process can be accomplished by using any acidic material, which can be either gaseous or liquid, capable of increasing the permeability and/or porosity of these tuffaceous streaks. Particularly effective means of acidization of formations under discussion include use of the materials and methods described in the Dilgren U.S. Patents 3,215,l99 and 3,297,090 and in the Dilgren et al. pending patent application Ser. No. 374,829, filed June 12, 1964, now Patent No. 3,307,630. Thus, the permeability and/or porosity of tulfaceous streaks or zones in oil shales can be rendered adequate to permit fiuid flow by emulsifying a mixture of an organic halide and Water with an emulsifying agent to form an emulsion that is temporarily stable under conditions existing in the tuffaceous streaks of the oil shale formation, being stable until the organic halide of the emulsion is hydrolyzed, subsequently pumping the emulsified mixture of the organic halide and water down an injection well, while the organic halide is hydrolyzing at rates that increase with increases in temperature, and in injecting the mixture of the hydrolyzing organic halide into the subterranean tuffaceous streaks in the oil shale formation at a rate such that the major portion of the reaction product, hydrogen halide, is formed within the formation. The hydrolyzing mixture is maintained in the formation for a time sufficient for the reaction product, hydrogen halide, to react with and dissolve the formation sufiiciently to increase the permeability thereof. Also, these tuffaceous streaks can be rendered permeable by injecting into a pair of wells in communication with said formation organic halides which are caused to react in situ with a solvating medium to form as one of the products of reaction, hydrogen halide. The process of treating a subterranean earth formation by contacting it with a liquid containing, comprising or even consisting essentially of an organic halide which is dissolved in or intimately contacted or commingled with a solvating medium, said organic halide and solvating medium being capable of reacting at the formation temperature to produce a hydrogen halide, and preferably being present in proportions sufiicient to produce enough hydrogen halide to cause acidization of the subterranean formations. Also, it is highly desirable that the organic halide and the solvating medium are selected and compounded to form a liquid mixture in which their rate of reaction is relatively slow at the ambient temperature at the well site but is significantly more rapid and comprises a preselected rate at the temperature of the formation that is to be treated.

Also a single, substantially homogeneous, acid-producing treating liquid comprising, containing or consisting of a reactive mixture of an organic halide and a solvating medium having a rate of reaction which Varies with temperature, said reagents being so selected that they react very slowly, while the treating liquid mixture is conveyed into the well and through a portion of the Well conduit, but will interact to form an active acid, namely hydrogen halide, at the temperature existing in the formation to be treated.

Although various organic halides may be used as one of the reactants which will form in situ the desired inorganic acid, it is preferable to employ aliphatic halides which may be either saturated or unsaturated provided they form by solvolysis the desired inorganic halide. A preferred class of these aliphatic halides are the saturated aliphatic monohalides and the unsaturated non-Vinyl monohalides. Illustrative examples of these compounds are n-propyl chloride, isopropyl chloride, t-butyl chloride, allyl chloride, crotyl chloride, methyl vinyl carbinyl chloride, as well as the corresponding bromides and iodides, e.g., allyl bromide, allyl iodide, t-butyl bromide and t-butyl iodide. The organic halide used as a reactant in the present process can be one containing functional groups other than halogen atoms. Examples of suitable polyfunctional organic halides include ethers such as bis-beta-chloroisopropyl ether, cyclic ethers such as epichlorohydrin, as well as a compound such as 1,3-dihydroxy-Z-chloropropane which is sufficiently hydrophilic to dissolve enough water to effect solvolysis reaction. Organic fluorides are generally less suitable as reactants in the present process because of their tendency to form insoluble calcium fluorides, but the organic fiuorides can be used whenever it is desirable to contact a calciumfree formation with a mixture of hydrogen fluoride and an oil-miscible solvent.

Although various organic halides may be used as one of the reactants which, according to the invention, will form in situ the desired inorganic acid, it is preferable to employ aliphatic halides which may be either saturated or unsaturated provided they form by solvolysis the desired inorganic halide. A preferred class of these aliphatic halides are the saturated monohalides and the allylic monohalides.

The solvating medium to be used in connection with the organic halide can be a compound which contains unshared electron pairs on an atom of the group consisting of oxygen and nitrogen atoms and is a liquid capable of reacting at the temperature of the subterranean formation with the organic halide to yield the corresponding hydrogen halide. The solvating medium should be substantially inert to and preferably non-reactive with the hydrogen halide in respect to altering the capability of the hydrogen halide to acidize the reservoir formation under the reservoir conditions and can include ketones, such as acetone and methyl ethyl ketone, nitriles, such as acetonitrile, propionitrile, cyclic ethers, such as the dioxanes and furans, etc.

In addition, the rate at which acid is produced can be also controlled by employing a catalyst capable of increasing the rate of acid production from an organic halide to a solvating medium.

Catalysts for this use include a water-soluble compound containing cuprous ions, such as cuprous chloride or cuprous nitrate.

Since the cuprous ions of the catalyst are readily oxidized to the non-catalytic cupric ion state by oxygen in the air, in the event that the water being used in carrying out the method of the present invention contains dissolved oxygen, it is preferable to also add a reducing agent to the mixture to prevent deactivation of any of the cuprous ions; which would result in decrease in rate of reaction for acid formation in the well or adjacent formation. One of the best materials found for use with the method of the present invention is hydrazine. The hydrazine not only acts as an oxygen scavenger in the water but is also capable of reducing the non-catalytic cupric ions to catalytic cuprous ions. This reduction is extremely slow in an acid medium, better at neutral conditions, and instantaneous in an alkaline medium. Ammonia or other water-soluble alkaline materials may be added to maintain the mixture alkaline at the beginning of the reaction.

Also organic halides which can react in situ with a solvating medium to form as one of the products, hydrogen halide can be used as the acidization reagent in the tuffaceous streaks of oil shales to increase their permeability. Gaseous hydrochloric acid may also be attractive for use in the present process. A gaseous material will flow through a slightly permeable formation more rapidly than a liquid.

The acidizing fluid as described is injected through wells penetrating the tuffaceous streaks of oil shale at a pressure normally less than the fracturing pressure and at a rate not dependent upon the creation of a fracture between the connecting pair of wells. The permeable zone thus formed is preferably not fractured until after acidizationof the formation has established sufficient permeability for a significant amount of fluid communication between wells, if fracturing appears to be attractive or desirable to improve or increase fluid communication.

Once a permeable and/or porous horizontal channel connecting a pair of wells penetrating an oil shale formation has been established, various thermal, pyrolysis, or explosive means such as hot fluid injection, eg., steam, hot water and mixtures thereof, hot gases, e.g., air, gaseous hydrocarbons such as hot hydrogen sulfide and mixtures of hydrocarbons and hydrogen sulfide; solvents, e.g., aliphatic and aromatic liquid hydrocarbons, such as benzene, xylene, kerosene, etc., said solvents may be hot or cold as well as conventional in situ combustion means such as injecting thermal energy to selected portions of the formation as well as variousother means as described on pages 95-104 of the World Oil issue of January 1965 and U.S. Patents 3,105,545; 3,150,715; 3,208,516; 3,221,810 and 3,250,328 as well as explosives (liquid or solid) can be employed for fluidizing materials for recovery through the production well and processing it for oil recovery.

The enumerated and other objects of the invention and details of the inventive process will become more apparent when viewed in light of the following description and accompanying illustration wherein:

The drawing diagrammatically illustrates a vertical section of'an oil shale formation containing tutfaceous streaks therein which are rendered permeable and porous by the acidizing process of the present invention and penetrated by a pair of wells.

Referring to the drawing, is the ground surface of the overburden 11 above an oil shale 12 containing tufaceous streaks 13 and 13a, said formations being penetrated by at least one pair of wells 14 and 15. Wells 14 and 15 are provided with casing strings 16 and 17 which contain valved lines 20 and 21. Within the casing strings are tubings 18 and 19, extending into the oil shale formation containing tutfaceous streaks therein, which are provided with valved lines 22 and 23. In the annular spaces between casings 16 and 17 and tubings 18 and 19 fixed packers 24 and 25 at the lower ends of the tubings are provided below the tuiaceous streaks. Removable packers 26 and 27 are provided in said annular spaces above some of the tuffaceous streaks. Casings 16 and 17 are provided with ports 28, 28a, 29 and 29a and tubings 18 and 19 are provided with ports 30 and 31, respectively.

In carrying out the process of the present invention acidizing fluids such as are described in the above-mentioned Dilgren patents or copending application are injected through either or both valved lines 22 and/or 23 into tubing strings 18 and/or 19 and forced to ow through ports 30 and/or 31 and through ports 28a and/ or 29a into the tuifaceous streaks zones 13 and 13a of formation 12. The acidizing fluids are injected under suitable conditions, time, temperature and pressure until permeable communication between wells 14 and 15 has been established as evidenced by permeable and/or porous channels 13 and 13a.

Once the permeable channels 13 and 13a in the oil shale 12 have -been established by acidizing, thus establishing communication between wells 14 and 15, shale oil can be recovered by using thermal energy, such as steam or underground combustion energy, or solvent production processes. In such cases well 14 can serve as an injection well and well a production well. [n cases where packers 26 and 27 are removable packers they can be removed and an injection fluid such as steam or mixtures of hot water and steam or combustible gases can be injected into formation 12 through lines 20 and/ or 22 so as to heat formation 12 suiiiciently to cause fluidization of the shale oil and cause it to ow into the permeable and/ or porous zones 13 and 13a through which they are driven by the injection fluids from well 14 to production well 15 and recovered above ground through valved lines 21 and/or 23. If the packers 26 and 27 are fixed then the injectionfluids are injected through valved line through ports 28 into formation 12 wherein the injection uids heat formation 12 sutliciently to fluidize the oil and cause it to ow into channels 13 and 13a which the oil is forced into production well 15 and recovered through valved lines 21 and/ or 23.

The oil recovery means used employing the injectionproduction wells mentioned can be any known in the art and particularly those made reference to above.

EXAMPLE TABLE I.--PROPERTIES (II'FFACEOUS ZONES IN OIL Solubles at F., percent wt.

In 15% HCl formed from allyl chlo- Permeabilride soluity, md. In water tion reaction Well Depth, ft.:

It will be appallent that modifications and variations as to acidizing techniques, acid materials used, as well as recovery of shale oil once permeable horizontal channel communication between wells have been established, will be evident to those skilled in the art and it is intended to Cover the modifications which fall within the scope of the appended claims.

I claim as my invention:

1. A method of recovering oil from underground oil shale formations containing tutfaceous streaks compris- (a) penetrating such formations with at least one production well and at least one injection well spaced from one another;

(b) establishing the location of tuffaceous streaks in the oil shale which extend between the injection and production wells;

(c) isolating a section of said injection well adjacent one of said thus-located streaks and injecting acidforming fluid through said isolated section of the injection well into the tuffaceous streaks and maintaining said acid-forming fluid therein under pressure and temperature conditions until `permeable horizontal channel communication is established between the injection and production wells; A

(d) injecting a thermal driving flid itbI the permeabilized oil shale formation to cause recoverable uidizable materials to move through the permeable channel toward the production well; and

(e) recovering above ground the fluidizable materials from the production well.

2. A method of claim 1 wherein the acid forming uid is a liquid solution containing an aliphatic monohalide capable of releasing hydrogen halide at a controlled rate and in sufficient amounts and concentrations to form permeable channels in the tuffaceous streaks in oil shale which channels are in communication with a pair of wells.

3. The method of claim 1 wherein the aliphatic monohalide is allyl chloride.

References Cited UNITED STATES PATENTS 2,804,145 8/1957 Holbrook 166-10 3,075,463 1/1963 Eilers et al. 166-36 3,246,693 4/ 1966 Crider 166-11 X 3,284,281 11/ 1966 Thomas 166-40 X 3,297,090 1/ 1967 Dilgren 166-38 (Other references on following page) 7 UNITED STATES PATENTS 5/1967 Strubhar 166-11 10/1967 Slusser 166-40 X 10/ 1967 Strange et a-I. 11/1967 Putman 166-11 X OTHER REFERENCES McKee, Ralph H., et a1.: A Chemical Examination of the Organic Matter in Oil Shales. In Quarterly of the Colo. School of Mines, 18(1), Supp. A, January 1923, pp. 29-3'2. TN870.M2.

CHARLES lE. OCONNELL, Primary Examiner I. A. CALVERT, Assistant Examiner U.S. C1. X.R. 

